ABSTRACT: Cigarette smoking induces oxidant stress in the lung and is the major risk factor for chronic obstructive pulmonary disease (COPD). We have shown that in the human lung, chronic cigarette smoking induces endoplasmic reticulum (ER) stress, a condition in which the capacity to fold nascent proteins cannot keep pace with the rate of protein synthesis. Moreover, our preliminary data indicate that the lungs of chronic cigarette smokers manifest a compensatory response termed the "unfolded protein response" (UPR) that restores ER protein homeostasis and enhances oxidant defense. We also found that cigarette smoke specifically activates the UPR-sensor, PERK (protein kinase R-like ER resident kinase) and its signaling pathway which up-regulates expression of the master anti-oxidant transcription factors, Nrf2 and ATF-4. Most importantly, our preliminary data in a small sample of subjects with advanced COPD (GOLD stage 3-4) suggest that a classic UPR may not occur in the lungs of individuals with advanced COPD. Based on these data, we hypothesize that the UPR, acting through the PERK signaling pathway, protects the lungs against cigarette smoke-induced oxidant stress and that subjects with advanced COPD have little or no UPR response to cigarette smoke. Accordingly, the specific aims of this 2 year project are to compare in active cigarette smokers with (i.e., GOLD 1-3;n=20) and without COPD (i.e., GOLD 0;n=20): 1). the magnitude of the UPR;and 2) the expression of Nrf2/ ATF-4, and the PERK-regulated initiator of apoptosis, CHOP. A group of never-smokers (n=10) will serve as further control. Expression of the hallmark UPR proteins, GRP78, calreticulin, calnexin and protein disulfide isomerase (PDI) as well as PERK effector proteins will be quantitated in fresh frozen lung samples. Levels of these UPR proteins will be correlated with the severity of COPD. This RFA involving the Lung Tissue Research Consortium (LTRC) provides the resources needed to carry out this aim. A better understanding of the cigarette smoke-induced UPR in subjects with and without COPD should enhance our understanding of the pathogenesis of this disease and facilitate development of novel treatments. (End of Abstract) PUBLIC HEALTH RELEVANCE: Narrative: Cigarette smoking is a risk factor for chronic obstructive pulmonary disease (COPD), a disease characterized by inflammation, and lung cell death. However, the pathogenesis of this disease remains incompletely understood and current therapies are inadequate. Our recent work showed that a novel biochemical pathway induced in the lung by cigarette smoking can be protective. This response and its biological consequences will be studied in human lungs. The results obtained are expected to improve our understanding of cigarette smoke-related lung disease and contribute to the development of new and better treatments.